i965: Handle scratch accesses where reladdr also points to scratch space

i965: Handle scratch accesses where reladdr also points to scratch space

This is a problem when we have IR like this:

(array_ref (var_ref temps) (swiz x (expression ivec4 bitcast_f2i
   (swiz xxxx (array_ref (var_ref temps) (constant int (2)) ) )) )) ) )

where we are indexing an array with the result of an expression that
accesses the same array.

In this scenario, temps will be moved to scratch space and we will need
to add scratch reads/writes for all accesses to temps, however, the
current implementation does not consider the case where a reladdr pointer
(obtained by indexing into temps trough a expression) points to a register
that is also stored in scratch space (as in this case, where the expression
used to index temps access temps[2]), and thus, requires a scratch read
before it is accessed.

v2 (Francisco Jerez):
 - Handle also recursive reladdr addressing.
 - Do not memcpy dst_reg into src_reg when rewriting reladdr.

v3 (Francisco Jerez):
 - Reduce complexity by moving recursive reladdr scratch access handling
   to a separate recursive function.
 - Do not skip demoting reladdr index registers to scratch space if the
   top level GRF has already been visited.

v4 (Francisco Jerez)
 - Remove redundant checks.
 - Simplify code by making emit_resolve_reladdr return a register with
   the original src data except for reg, reg_offset and reladdr.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89508
Reviewed-by: Francisco Jerez <currojerez@riseup.net>